1. Field of the Invention
The present invention relates to a laser processing method and apparatus for applying a laser beam to a workpiece having a plurality of members to thereby form a laser processed groove on the workpiece.
2. Description of the Related Art
As well known in the art, in a semiconductor device fabrication process, a plurality of crossing division lines called streets are formed on the front side of a substantially disk-shaped semiconductor substrate to thereby partition a plurality of regions where a plurality of devices such as ICs and LSIs are respectively formed, thus constituting a semiconductor wafer. The semiconductor wafer is cut along the streets to thereby obtain the individual semiconductor devices. Cutting of the semiconductor wafer along the streets is usually performed by using a cutting apparatus. This cutting apparatus includes a chuck table for holding the semiconductor wafer as a workpiece, cutting means for cutting the semiconductor wafer held on the chuck table, and moving means for relatively moving the chuck table and the cutting means. The cutting means includes a spindle adapted to be rotated at high speeds and a cutting blade mounted on the spindle. The cutting blade is composed of a disk-shaped base and an annular cutting edge mounted on a side surface of the base along the outer circumference thereof. The cutting edge is formed by bonding diamond abrasive grains having a grain size of about 3 μm by electroforming so that the thickness of the cutting edge becomes about 20 μm, for example.
In recent years, a semiconductor wafer intended to improve the processing performance of devices such as ICs and LSIs has been put into practical use. This semiconductor wafer is composed of a semiconductor substrate such as a silicon wafer and a low-permittivity insulator film (Low-k film) formed on the front side of the semiconductor substrate. Examples of the Low-k film include an inorganic film of SiOF, BSG (SiOB), etc. and an organic film such as a polymer film of polyimide, parylene, etc.
Further, there has been put into practical use a semiconductor wafer having a configuration such that a plurality of testing metal patterns called test element group (Teg) for testing the function of the devices are partially provided on the Low-k film in the streets.
However, the Low-k film is formed as a multilayer film like mica and it is very brittle. Accordingly, when this semiconductor wafer having the Low-k film is cut along the streets by using the cutting blade, there arises a problem such that the Low-k film may be separated and this separation may reach the devices to cause fatal damage to the semiconductor devices. Further, in the case of the semiconductor wafer such that the testing metal patterns called test element group (Teg) for testing the function of the devices are partially provided on the streets, there arises a problem such that when the semiconductor wafer is cut along the streets by using the cutting blade, burrs may be generated because the metal patterns are formed of a tough metal such as copper, causing chipping on the side surfaces of each device to result in a degradation in quality of each device.
To solve the above problems, there has been proposed a wafer dividing method including the steps of applying a laser beam to the semiconductor wafer along each street to form a laser processed groove along each street, thereby removing the Low-k film and the Teg on each street and next cutting this area where the Low-k film and the Teg have been removed, by using a cutting blade. However, in the case that the Low-k film and the Teg are provided on each street, the Low-k film and the Teg are removed by applying the laser beam under different processing conditions. Accordingly, this wafer dividing method includes a Teg removing step of preliminarily detecting the position of the Teg to make coordinate data and then applying a laser beam to the Teg according to this coordinate data to thereby remove the Teg and a Low-k film removing step of applying the laser beam to the Low-k film on each street to thereby remove the Low-k film (see Japanese Patent Laid-Open No. 2005-118832, for example).